The invention is in a process for the removal of cholesterol and cholesterol esters from egg yolk with the aid of .beta.-cyclodextrin as a complexing agent. Cholesterol and cholesterol esters, denoted cholesterol derivatives in the following, are lipophilic substances which occur in numerous foodstuffs of animal origin such as e.g. egg yolk, meat, animal fats etc.
The intake of very large amounts of cholesterol derivatives through the diet is known to represent an increased risk factor for arteriosclerosis or coronary heart disease. For this reason the food industry is interested in significantly reducing cholesterol derivatives in high-fat foodstuffs of animal origin. A fundamental problem in this is to preserve the sensorial and nutritional physiological properties of the foodstuffs to a large extent.
A number of processes for isolating cholesterol derivatives is already known; however, these processes are, unsuitable for reducing the content of cholesterol derivatives in foodstuffs because undesired changes in these properties occur which are due to chemical changes in important constituents of the starting material (such as e.g. proteins, triglycerides etc.).
A relatively mild process which has only recently become known uses CO.sub.2 high pressure extraction to remove cholesterol derivatives (cf. V. Krukonis, Supercritical Fluid Processing, International Symposium on Supercritical Fluids, Nice, 1988, and A. Bude and D. Knorr, Reduction of Cholesterol in Egg Powder and Whole Eggs by Extraction with Supercritical Carbon Dioxide, Fifth International Congress on Engineering and Food, Cologne, 1989).
These processes are distinguished by the physiological harmlessness of the extraction agent (CO.sub.2), working at high pressure is however, technically quite complicated. In addition these processes do not allow cholesterol derivatives to be selectively removed under mild conditions because triglycerides are also extracted.
Selectivity can in principle be improved by increasing the temperature but this has a negative effect on the loading of CO.sub.2 with cholesterol derivatives and on the quality of the product obtained.
Another known process for removing cholesterol derivatives is the complexation of these substances with .beta.-cyclodextrin. Thus according to EP-A 0 326 469 egg yolk powder is for example stirred with .beta.-cyclodextrin for 5 hours at 40.degree. C. after its homogenization with water and the complex obtained is separated by centrifugation, However, the cholesterol contents may only be reduced to a maximum of 74% of the initial value in this way.
A significant improvement with regard to reducing cholesterol is possible according to the process of DE-OS 39 28 258 in which only the egg yolk plasma fraction, which can be obtained from egg yolk using a demulsifying agent such as e.g. water after centrifuging the LDL granular fraction, is admixed with .beta.-cyclodextrin and not the entire egg yolk. Subsequently the egg yolk plasma treated in this way is again combined with the LDL granular fraction after separating the .beta.-cyclodextrin and its complexes.
However, in some cases it is difficult to separate the egg yolk plasma fraction from the LDL granular fraction and from the .beta.-cyclodextrin cholesterol complex. In order to solve this problem it was proposed in DE-OS 40 13 367 as well as WO 91/11 114 to admix the egg yolk with a diluted aqueous solution of ammonium carbonate or sodium chloride before the complexation step with .beta.-cyclodextrin in order to prevent the emulsion breaking down and precipitation of the LDL granular fraction.
A disadvantage of this process is however, the fact that it is very difficult to completely remove the added salts from the egg yolk mixture. Apart from the fact that for this reason the process soon becomes uneconomical, the reduced-cholesterol egg yolk products produced in this way usually have a higher content of sodium or ammonium ions which is undesirable with regard to nutritional physiology.